Krauthammer said it's clear now that "there's not a person in Washington" who thinks Trump's claims are true and the president is risking his credibility by continuing to pursue it.

"He seems to have a belief in conspiracy theories. This is, after all, a man who said Ted Cruz's father was involved in some way with Lee Harvey Oswald. That's 'Twilight Zone' stuff," he noted.

Trump made the explosive claims in a series of tweets on the morning of March 4. In an interview Wednesday, Carlson pressed Trump on why he made the claims without first obtaining evidence to back them up.

Trump still claimed there is "a lot" of evidence, citing news reports and saying he was referring to broader surveillance in his tweets.

Krauthammer pointed out that if there were real proof, Trump could get it easily by calling top justice and intelligence officials.

He agreed with Carlson that there may have been "mishandling" of communications involving Americans and Russian officials under surveillance, but that Trump's claims are distracting from those issues.